Coordination polymerization of olefinically unsaturated monomers is well known and has led to the great proliferation in modern society of elastomeric and plastic compositions of matter, such as polyethylene, polypropylene, and ethylene propylene rubber. Early pioneers utilized transition metal compounds with such activators as aluminum alkyls and later development extended this work to bulky ligand-containing (e.g., .eta..sup.5 -cyclopentadienyl) transition metals ("metallocenes") with activators such as alkyl alumoxanes. The most recent developments have shown the effectiveness of ionic catalysts comprised of metallocene cations activated by non-coordinating anions, see for example EP-A-277,004 and U.S. Pat. No. 5,198,401. These references described protonation of metallocene compounds by anion precursors to form stable ionic catalysts.
The ionic catalysts of the prior art have shown to varying degrees significant sensitivity to catalyst poisons present in monomer feed streams or in recycled fluid streams in the polymerization process and have posed problems for use with inert oxide supports that typically have either or both of retained moisture or polar hydroxyl groups. Accordingly processes have been developed to utilize poison scavenging compounds, for example alkyl aluminiums or alumoxanes, for solution polymerization and to remove or neutralize polar groups retained in or on metal oxide supports. See, for example, U.S. Pat. No. 5,153,157, describing Group-IIIA metal scavenger compounds, and WO-A-91/09882, WO-A-94/00500 and WO-A-94/03506 describing supporting techniques utilizing similar compounds. U.S. Pat. No. 5,206,197 describes enhanced polymerization of styrene where the ionic catalyst systems include a metal hydrocarbyl, and, which may be supported. All documents are referred to for description of metallocene compounds, ionic activators and useful scavenging compounds.
Supported catalysts based on the reaction of chromocenes with metal (M) oxides, suggested to yield a chromate or dichromate structure, --Cr(--O--M--).sub.2 or (--M--O--Cr--)(O)(--Cr--O--M--), are also a well-known class of supported metallocene catalysts found to be useful particularly for linear polyethylene by any of solution, slurry or gas phase commercial processes. See, for example, "Supported Chromium Catalyst for Ethylene Polymerization", McDaniel, Advances in Catalysis 1985, 33, 47-97. Silica is a less preferred support due to a lower reactivity than, for example, aluminum phosphate, typically no other activator is required, and the metal center of the metallocene is covalently bound through the oxo-linkage (--O--) to the support metal/metalloid.
Additionally, U.S. Pat. No. 5,427,991 and equivalent WO-A-93/11172 describe the chemical bonding of non-coordinating anionic activators to supports so as to prepare polyanionic activators that when used with the metallocene compounds avoid problems of catalyst desorption experienced when ionic catalysts physically adsorbed on metal oxide supports are utilized in solution or slurry polymerization. The supports are core components of inert monomeric, oligomeric, polymeric or metal oxide supports which have been prepared so as to incorporate chemically bound non-coordinating anions. The teaching of the preparation of polyanionic activators from metal oxides (FIG. 8) entails the reaction of a hydroxylated silica surface with silane coupling agents at least some of which contain halolaryl moieties which can be lithiated to form chemically bound arylithium groups. These are subsequently treated with the bulky metalloid precursor trisperfluorophenylboron (B(pfp).sub.3) and subjected to an ion exchange reaction with diemthylanilinium hydrochloride ([DMAH].sup.+ [Cl].sup.-) so as to prepare a silica surface having covalently linked activator groups of [DMAH].sup.+ [(pfp).sub.3 B].sup.-. The examples illustrate the bulk polymerization of polypropylene using hydrocarbyl support based polyionic catalyst systems in batch autoclave reactors.
There is a need to address further both the preparation of ionic catalyst systems on supports and a need to find support catalysts that are not subject to problems in the polymerization process leading to reactor instability from over-production, fouling of polymerization equipment surfaces, and unwanted preparation of polymer particles of poor morphology not suited to efficient polymer production on an industrial scale.